1. Field of Invention
This invention relates to novel sweeteners. In particular, the invention relates to metal complexes of dipeptide sweeteners which show improved dissolution rate, solubility and temperature stability without significant loss of sweetness.
It has been found that certain dipeptide compounds possess an intense sweetness. Examples of these compounds are set forth in U.S. Pat. Nos. 3,475,403 issued Oct. 28, 1969, 3,492,131 issued Jan. 27, 1970, and in the following foreign patents; Republic of South Africa Pat. Nos. 695,083 published July 12, 1969, 695,910 published Aug. 14, 1969 and German Pat. No. 2,054,545 published May 19, 1971. Generically, these compounds are represented by the formula: ##STR1## wherein R represents the lower alkyls, lower alkyaryls and cycloalkyls, n stands for integers 0 through 5, R.sub.1, represents (a) phenyl group, (b) lower alkyls, (c) cycloalkyls, (d) R.sub.2
where R.sub.2 is hydroxy, lower alkoxy, lower alkyl, halogen, (e) S(O).sub.m (lower alkyl) where m is 0, 1 or 2 and provided n is 1 or 2, (f) R.sub.3
where R.sub.3 represents an hydroxy or alkoxy and (g) single or double unsaturated cycloalkyls with up to eight carbons. Most suitable among these compounds are the lower alkyl esters of aspartyl phenylalanine (U.S. Pat. No. 3,492,131) wherein the stereochemical configuration is DL-L, L-L, DL-DL, or L-DL. Illustrative of the lower alkyl esters are methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl and the branched chain groups isomeric therewith, with the methyl ester being the most preferred embodiments, said patents which are herein incorporated by reference.
These dipeptides of Formula I have significant sweetening properties. Problems have arisen, however, with the use of these compounds in dry systems in that their rate of solution into aqueous medium is markedly slower than sucrose, the absolute solubility is poor and the compounds readily decompose above 80.degree. C. as exemplified by the methyl ester of L-aspartyl-L-phenylalanine (APM).
2. Description of the Prior Art
Dipeptide sweeteners are well known in the art as described above. While the problem of stability, dissolution rate and solubility are well documented, little has been done to overcome the problem. In U.S. Pat. No. 4,139,639 a chewing gum composition is described in which APM is fixed in gum Arabic and/or the reaction product of a compound containing a polyvalent metallic ion, with an ungelatinized starch acid-ester of a substituted dicarboxylic acid thus forming an encapsulated APM-gum composition which increases the stability of the APM. In addition, U.S. Pat. No. 4,029,701 describes the hydrohalide salts of dipeptide sweeteners as being an improvement in terms of the rate of dissolution. But the hydrochloride salts do not exhibit heat stability or appreciable increases in solubility. Glickman, in U.S. Pat. No. 3,761,288 describes a method for spray drying aspartame which increases the solubility of aspartame and enables aspartame to be spray dryed at 100.degree. C. or above without appreciable decomposition but only if the contact time is short as in normal spray drying techniques.